Identification marks for identifying persons or articles are used in many areas of daily life. Identification marks based on bar codes are used in accordance with the prior art, but they are personnel-intensive and thus expensive in application since they have to be read using an optical reader that has to be operated by a user. Moreover, bar code systems cannot be used practically in many areas of application of identification marks (for example empty-theft systems in department stores).
“Radio Frequency Identification Tags” (RFID tags) are suitable for such applications. An RFID tag usually contains an antenna, a circuit for receiving and transmitting electromagnetic waves (transponder) and a signal processing circuit. Consequently, such an RFID tag is often constructed from a small silicon chip connected to an antenna applied on a plastic carrier.
An RFID tag enables data to be read or stored contactlessly. Such data are stored on RFID tags (clearly electronic labels). The stored data are read by means of electromagnetic waves that can be coupled into the RFID tag via the antenna.
Areas of use for an RFID tag include electronic merchandise protection systems for preventing theft, applications in automation technology (for example the automatic identification of vehicles in traffic in the context of toll systems), access control systems, cashless payment, ski passes, fuel cards, animal identification and applications in lending libraries.
RFID tags are often applied on a thin film, for example made of polyethylene terephthalate (PET). In order to supply the RFID tag with power and in order to couple out the data, an antenna is used and printed onto the film.
Connecting both ends of the antenna or coil to the chip requires two plated-through holes on the film.
Such an RFID tag 100 in accordance with the prior art is described below referring to FIG. 1.
FIG. 1 illustrates an RFID tag 100, the circuitry-active components of which are formed on a PET film 101. An electronic chip 102 is arranged on a first main surface 110, the two chin connections of the electronic chip being coupled to two antenna connections of an antenna 103. The antenna 103 is formed by printing a spiral aluminum structure onto the first main surface 110. Furthermore, a first plated-through hole 104 and a second plated-through hole 105 are formed in the PET film 101, and are filled with electrically conductive material in order to resistively couple one of the chip connections to one of the antenna connections using a rear-side contact-making element 106.
The fitting of the plated-through holes 104, 105 causes a considerable proportion of all the assembly costs in the case of the RFID tag 100 in accordance with the prior art.
For these and other reasons, there is a need for the present invention.
The present invention provides an identification data carrier. In one embodiment the identification data carrier of the invention contains a carrier substrate, an electronic chip fitted on and/or in the carrier substrate, a transmitting/receiving antenna formed on and/or in the carrier substrate and serving for transmitting and for receiving electromagnetic radiation, and a first capacitance, the chip being capacitively coupled to the transmitting/receiving antenna by means of the first capacitance.
A basic idea of the invention can be seen in the fact that, in the case of an identification data carrier (for example an RFID tag), an electronic chip is coupled capacitively to a transmitting/receiving antenna, rather than being coupled resistively as in accordance with the prior art. On account of the realization of a capacitive coupling by means of the first capacitance, that is to say by means of a capacitor, the provision of cost-intensive plated-through holes becomes dispensable.
The components of the first capacitance, the chip and the transmitting/receiving antenna may be formed on one main surface or on both main surfaces of a carrier substrate of the identification data carrier according to the invention, it being possible for the plated-through passages to be obviated on account of the dispensability of a resistive coupling. As a result, the identification data carrier of the invention can be manufactured considerably more favorably. The term main surfaces denotes the two areas of the carrier substrate which form by far the predominant proportion of the surface area of the preferably filmlike, planar carrier substrate.
By way of example, two electrically conductive structures may be formed as capacitor plates of the first capacitance on different surface regions of one main surface of the carrier substrate or alternatively on opposite main surfaces of the carrier substrate. With the use of a radiofrequency exciting electromagnetic radiation that can be absorbed by the transmitting/receiving antenna, the capacitive coupling element has a sufficiently low impedance, so that it clearly approximately forms a short circuit.
In other words, the invention avoids the need to provide plated-through passages in the case of an RFID tag film by means of the provision of at least one capacitor. Consequently, instead of conventional plated-through holes, capacitors are constructed in accordance with the invention in order to couple an electronic chip to a transmitting/receiving antenna in the case of an identification data carrier.
If a capacitor is constructed instead of such plated-through holes, then a series resonant circuit comprising the first capacitor (or comprising two or more capacitors) and a coil results. If the series resonant frequency of this circuit is far less than the parallel resonant frequency, the resonant circuit acts substantially inductively and the capacitors are then to be regarded virtually as a short circuit.
If the carrier substrate, which may be realized as a film, is very thin (for example 30 μm) and has a sufficiently large value of the relative permittivity (for example εr=4), even relatively large capacitances can be produced very easily. If the capacitance is nevertheless too small for a specific application, then the capacitance can be increased by means of insipiently etching the film in a region in which two capacitor elements of the first capacitance lie opposite one another and are separated by the insipiently etched film. The capacitance may also be additionally increased by means of using a particularly thin film or a film material having a value of the relative permittivity εr that is sufficiently high.
The solution according to the invention is particularly of interest precisely at increasing frequencies (in the radiofrequency range and above). The higher the RFID operating frequency, the smaller the capacitor can be chosen to be and the less additional area is required.
In one embodiment, the electronic chip, the transmitting/receiving antenna and the first capacitance may be formed on the same main surface of the carrier substrate. In this case, the production costs are reduced to a particularly great extent since only a single side of the carrier substrate has to be processed.
In accordance with the embodiment just described, the first capacitance may have a first electrically conductive structure and a second electrically conductive structure arranged at a distance from the first electrically conductive structure, the first electrically conductive structure being coupled to a first chip connection of the chip, the second electrically conductive structure being coupled to a first antenna connection of the transmitting/receiving antenna, and a second chip connection of the chip being coupled to a second antenna connection of the transmitting/receiving antenna. In accordance with this refinement, a coupling is created between chip, transmitting/receiving antenna and the first capacitance, which are all formed on a common main surface of the carrier substrate, as a result of which the processing costs are reduced to a particularly great extent.
The identification data carrier may have a second capacitance, the chip being capacitively coupled to the transmitting/receiving antenna by means of the first capacitance and by means of the second capacitance.
In accordance with this embodiment, the electronic chip may be formed on a first main surface of the carrier substrate, and the transmitting/receiving antenna may be formed on a second main surface of the carrier substrate, said second main surface lying opposite the first main surface.
In this embodiment, a coupling between the electronic chip and the transmitting/receiving antenna on the two different main surfaces of the carrier substrate is effected by means of a capacitive coupling element, one part of which is provided on the first main surface and another part of which is provided on the second main surface. In this way, the components (area A) of the capacitor are separated from one another by the carrier substrate and are thus provided at a distance d from one another, so that, in accordance with the equationC=ε0εrA/d  (1)a particularly high value of the capacitance C of the capacitor and thus a good capacitive coupling can be achieved. This is because, in accordance with this refinement, the material of the carrier substrate can be chosen in such a way that the value of the relative permittivity εr is particularly high. Moreover, the distance between the capacitor elements, that is to say the thickness d of the carrier substrate, can be chosen to be small enough to achieve a sufficiently large capacitance. The areas A of the capacitor elements can be chosen to be large enough to set the value of C as desired. The value of the electric field constant is ε0=8.85·10−12F/m.
In the case of the identification data carrier, the first capacitance may have a first electrically conductive structure formed on the first main surface and a second electrically conductive structure arranged on the second main surface at a distance from the first electrically conductive structure, the second capacitance having a third conductive structure formed on the first main surface and a fourth conductive structure arranged on the second main surface at a distance from the third electrically conductive structure, the first electrically conductive structure being coupled to a first chip connection of the chip, the third electrically conductive structure being coupled to a second chip connection of the chip, the second electrically conductive structure being coupled to a first antenna connection of the transmitting/receiving antenna, and the fourth electrically conductive structure being coupled to a second antenna connection of the transmitting/receiving antenna.
In this embodiment, a particularly good capacitive coupling is achieved using two capacitances provided on opposite main surfaces of the carrier substrate.
The transmitting/receiving antenna may be formed as a planar spiral structure. Cost-effective processing is accordingly possible since such a transmitting/receiving antenna can be printed onto the carrier substrate in a simple manner.
At least one of the electrically conductive structures may be formed as an interrupted ring structure, that is to say as an essentially ringlike structure that is separated in a ring section. A ring is understood to be a circular ring, a rectangular ring, etc.
The carrier substrate may be a plastic film, in particular a PET film (polyethylene terephthalate).
The carrier substrate may be free of a passage hole. The processing costs can be considerably reduced by means of saving passage holes.
The electronic chip may be a silicon chip. To put it another way, the electronic chip may be formed as an integrated circuit using silicon technology, so that it is possible to have recourse to the mature standard processes of silicon microtechnology.
The identification data carrier may be set up as an RFID tag (“Radio Frequency Identification Tag”).
Different components of the first capacitance may be separated by the carrier substrate, and the carrier substrate may have a smaller thickness in a region in which said components are formed than in other regions. To put it another way, the carrier substrate may be thinned in a region in which the components are formed. By means of thinning the carrier substrate in a region in which capacitor elements are formed on two opposite main surfaces of the carrier substrate, it is possible, in accordance with equation (1), by means of reducing the thickness d, to greatly increase the capacitance and thus to improve the capacitive coupling.